Theorem tsbi2 36908

Description: A Tseitin axiom for logical biconditional, in deduction form. (Contributed by Giovanni Mascellani, 24-Mar-2018.)

Assertion

Ref	Expression
tsbi2	⊢ (𝜃 → ((𝜑 ∨ 𝜓) ∨ (𝜑 ↔ 𝜓)))

Proof of Theorem tsbi2

Step	Hyp	Ref	Expression
1		pm5.21 824	. . . 4 ⊢ ((¬ 𝜑 ∧ ¬ 𝜓) → (𝜑 ↔ 𝜓))
2	1	olcd 873	. . 3 ⊢ ((¬ 𝜑 ∧ ¬ 𝜓) → ((𝜑 ∨ 𝜓) ∨ (𝜑 ↔ 𝜓)))
3		pm4.57 990	. . . . 5 ⊢ (¬ (¬ 𝜑 ∧ ¬ 𝜓) ↔ (𝜑 ∨ 𝜓))
4	3	biimpi 215	. . . 4 ⊢ (¬ (¬ 𝜑 ∧ ¬ 𝜓) → (𝜑 ∨ 𝜓))
5	4	orcd 872	. . 3 ⊢ (¬ (¬ 𝜑 ∧ ¬ 𝜓) → ((𝜑 ∨ 𝜓) ∨ (𝜑 ↔ 𝜓)))
6	2, 5	pm2.61i 182	. 2 ⊢ ((𝜑 ∨ 𝜓) ∨ (𝜑 ↔ 𝜓))
7	6	a1i 11	1 ⊢ (𝜃 → ((𝜑 ∨ 𝜓) ∨ (𝜑 ↔ 𝜓)))

Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 205   ∧ wa 397   ∨ wo 846

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem depends on definitions:  df-bi 206  df-an 398  df-or 847

This theorem is referenced by:  tsxo2  36912  mpobi123f  36936  mptbi12f  36940  ac6s6  36946